Asphalt composition containing highly coupled radial polymers

ABSTRACT

A bituminous composition comprising a compatible bituminous component and a completely non-tapered radial block copolymer of a conjugated diolefin and a vinyl aromatic hydrocarbon wherein the polymer has from 3 to 6 arms, a molecular weight of from 150,000 to 400,000, a coupling efficiency of at least 95 percent, and a polyvinyl aromatic hydrocarbon blockiness of at least 98.5%.

BACKGROUND OF THE INVENTION

The present invention relates to asphalt compositions containingpolymers for modification of the properties of the asphalt. Moreparticularly, this invention relates to such compositions containing newpolymers which impart lower processing viscosity to the asphalt whilemaintaining the desired high softening point for the composition.

Asphalt is a common material utilized for the preparation of paving androofing materials and also for coatings such as pipe coatings and tankliners. While the material is suitable in many respects, it inherentlyis deficient in some physical properties which it would be highlydesirable to improve. Efforts have been made in this direction byaddition of certain conjugated diene rubbers, ethylene containingplastics like EVA and polyethylene, neoprene, resins, fillers and othermaterials for the modification of one or more of the physical propertiesof the asphalt. Each of these added materials modifies the asphalt inone respect or another but certain deficiencies can be noted in allmodifiers proposed. For example, some of them have excellent weatherresistance, sealing and bonding properties but are often deficient withrespect to warm tack, modulus, hardness and other physical properties;and some of them improve only the high temperature performance ofasphalt, some only improve the low temperature performance of asphalt,while some lack thermal stability or mixing stability with asphalt.

Since the late 1960s, diene polymer rubbers such as styrene-butadienerubber and styrene-rubber block copolymers such asstyrene-butadiene-styrene and styrene-isoprenestyrene block copolymershave been used to dramatically improve the thermal and mechanicalproperties of asphalts. Practical application of the rubber additionapproach requires that the blended product retain improved propertiesand homogeneity during transportation, storage and processing. Long termperformance of elastomer-modified asphalts also depends on the abilityof the blend to maintain thermal and chemical stability.

Such polymers have been found to be very advantageous but in some enduses, such as roll roofing membranes, high processing viscosity ofblends of asphalt and such polymers leads to reduced manufacturingrates. Other attempts at lowering the processing viscosity, such asreducing molecular weight or polymer content or adding oil, have provedto be undesirable because the softening point of the composition waslowered to such an extent that adequate slump resistance could not beachieved. Also, the processing stability of blends of some of thecommercially used polymers could advantageously be improved to provide awider processing window. Therefore, it can be seen that it would behighly advantageous to have a asphalt blend which is characterized inthat the ring and ball softening point is relatively high, at least 118°C. to 125° C., the processing viscosity is lower than currently possiblewith the popular commercially available materials, i.e., preferably lessthan 3000 centipoise, and the processing stability of the blend isimproved such that higher processing temperatures may be used.

SUMMARY OF THE INVENTION

This invention relates to a bituminous composition with improvedproperties over neat asphalt. The invention is a polymer modifiedbituminous composition which exhibits a better balance of properties,processability, softening point, and processing stability, than previouspolymer modified bituminous compositions. The bituminous compositioncomprises a compatible bituminous component and a completely non-taperedhighly coupled radial block copolymer of a conjugated diolefin and avinyl aromatic hydrocarbon. The radial polymer should have from 3 to 6arms, the coupling efficiency should be at least 95 percent, themolecular weight of the polymer should be from 150,000 to 400,000, andat least 98.5% of the vinyl aromatic hydrocarbon must be contained inthe vinyl aromatic hydrocarbon blocks. Specific applications of thiscomposition include roofing materials, coatings, hot melt asphaltconcrete and sealant compositions.

DETAILED DESCRIPTION OF THE INVENTION

Compatible asphalts should be used in the present invention. Asphaltswith high asphaltene contents, i.e. greater than 12%, because suchasphalts are generally incompatible with the polymer component.Asphaltenes are known to those skilled in the art. For purposes of thisapplication, asphaltenes make up the n-heptane insoluble fraction ofasphalt. While the polymers described herein have utility when used withincompatible asphalts, they achieve a performance advantage only withcompatible asphalts, i.e. those having an asphaltene content of 12% orless.

The bituminous component in the bituminous-polymer compositionsaccording to the present invention may be a naturally occurring bitumenor derived from a mineral oil. Also, petroleum derivatives obtained by acracking process, pitch and coal tar can be used as the bituminouscomponent as well as blends of various bituminous materials.

Examples of suitable components include distillation or "straight-runbitumens," precipitation bitumens, e.g. propane bitumens, blown bitumensand mixtures thereof. Other suitable bituminous components includemixtures of one or more of these bitumens with extenders such aspetroleum extracts, e.g. aromatic extracts, distillates or residues, orwith oils.

Polymers containing ethylenic unsaturation or both aromatic andethylenic unsaturation may be prepared using anionic initiators orpolymerization catalysts. Such polymers may be prepared using bulk,solution or emulsion techniques. In any case, the polymer containing atleast ethylenic unsaturation will, generally, be recovered as a solidsuch as a crumb, a powder, a pellet or the like, but it also may berecovered as a liquid such as in the present invention. Polymerscontaining ethylenic unsaturation and polymers containing both aromaticand ethylenic unsaturation are available commercially from severalsuppliers.

In general, when solution anionic techniques are used, copolymers ofconjugated diolefins and alkenyl aromatic hydrocarbons are prepared bycontacting the monomer or monomers to be polymerized simultaneously orsequentially with an anionic polymerization initiator such as group IAmetals, their alkyls, amides, silanolates, napthalides, biphenyls oranthracenyl derivatives. It is preferred to use an organo alkali metal(such as sodium or potassium) compound in a suitable solvent at atemperature within the range from about -150° C. to about 300° C.,preferably at a temperature within the range from about 0° C. to about100° C. Particularly effective anionic polymerization initiators areorgano lithium compounds having the general formula:

    RLi.sub.n

wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substitutedaromatic hydrocarbon radical having from 1 to about 20 carbon atoms andn is an integer of 1 to 4.

Conjugated diolefins which may be polymerized anionically include thoseconjugated diolefins containing from about 4 to about 24 carbon atomssuch as 1,3-butadiene, isoprene, piperylene, methylpentadiene,phenyl-butadiene, 3,4-dimethylo 1,3-hexadiene, 4,5-diethyl-1,3-octadieneand the like. Isoprene and butadiene are the preferred conjugated dienemonomers for use in the present invention because of their low cost andready availability. Alkenyl aromatic hydrocarbons which may becopolymerized include vinyl aryl compounds such as styrene, variousalkyl-substituted styrenes, alkoxy-substituted styrenes, vinylnapthalene, alkyl-substituted vinyl napthalenes and the like.

The block copolymers may be produced by any well known blockpolymerization or copolymerization procedures including the well-knownsequential addition of monomer techniques, incremental addition ofmonomer technique or coupling technique. As is well known in the blockcopolymer art, tapered copolymer blocks can be incorporated in themultiblock copolymer by copolymerizing a mixture of conjugated diene andvinyl aromatic hydrocarbon monomers utilizing the difference in theircopolymerization reactivity rates. However, such polymers are lessefficient compared to the polymers of this invention so they areexcluded from my invention. For the polymers of the present invention,the polymerization must be carried out so that at least 98.5% of thefree vinyl aromatic hydrocarbon is incorporated in the polyvinylaromatic hydrocarbon blocks and less than 1.5% is incorporated in thepolydiene blocks.

The present invention works with both unhydrogenated and hydrogenatedpolymers. Hydrogenated ones are useful in certain circumstances. Whileunhydrogenated diene polymers have a number of outstanding technicaladvantages, one of their principal limitations lies in their sensitivityto oxidation. This can be minimized by hydrogenating the copolymers,especially in the diene blocks. The hydrogenation of these polymers andcopolymers may be carried out by a variety of well established processesincluding hydrogenation in the presence of such catalysts as RaneyNickel, noble metals such as platinum, palladium and the like andsoluble transition metal catalysts. Titanium biscyclopentadienylcatalysts may also be used. Suitable hydrogenation processes which canbe used are ones wherein the diene-containing polymer or copolymer isdissolved in an inert hydrocarbon diluent such as cyclohexane andhydrogenated by reaction with hydrogen in the presence of a solublehydrogenation catalyst. Such processes are disclosed in U.S. Patent Nos.3,113,986, 4,226,952 and Reissue 27,145, the disclosures of which areherein incorporated by reference. The polymers are hydrogenated in sucha manner as to produce hydrogenated polymers having a residualunsaturation content in the polydiene block of less than about 20%, andpreferably as close to zero percent as possible, of their originalunsaturation content prior to hydrogenation.

These polymers may have a vinyl aromatic hydrocarbon content of 25 to 35percent so that they achieve adequate properties and are sufficientlycompatible with the asphalt. They should have a molecular weight of from150,000 to 400,000 so that adequate softening points may be achieved.The radial polymers should have from 3 to 6 arms because radial polymersexhibit lower viscosity than linear polymers at equal molecular weight.The coupling efficiency of the polymer must be at least 95 percent toensure high processing efficiency. The blockiness of the vinyl aromatichydrocarbon, as determined by nuclear magnetic resonance, should be atleast 98.5% for maximum efficiency.

If produced by sequential addition of monomer, the block copolymers havea very high coupling efficiency, usually close to 100%. Other processesrequire close control of the polymerization to ensure that high couplingefficiency is obtained. In the prior art, such as that exemplified byU.S. Pat. Nos. 3,595,941 and 3,468,972, the disclosures of which areherein incorporated by reference, the effort was always made to selectthe particular coupling agent or reaction conditions that resulted inthe highest coupling efficiency. Lower coupling efficiencies are desiredherein in order to produce adhesive compositions which adhere stronglyto difficult to adhere substances such as polyolefins, e.g.polyethylene. Coupling efficiency is defined as the number of moleculesof coupled polymer divided by the number of molecules of coupled polymerplus the number of molecules of uncoupled polymer. Thus, when producingan ABA linear polymer, the coupling efficiency is shown by the followingrelationship: ##EQU1## Coupling efficiency can be determinedtheoretically from the stoichiometric quantity of coupling agentrequired for complete coupling or coupling efficiency can be determinedby an analytical method such as gel permeation chromatography. Typicalprior art coupling efficiency is from about 80% to almost 100%. In U.S.Pat. No. 4,096,203, coupling efficiency is controlled from about 20% toabout 80%, preferably about 30% to about 70%. It is also within thescope of the present invention to blend polymers from processes ofdiffering coupling efficiency. For example, if a 60% efficiency isdesired, then polymers from processes having an 80% efficiency and a 40%efficiency may be blended together or a 100% triblock may be blendedwith a 100% diblock in a 60:40 ratio.

Molecular weights of linear polymers or unassembled linear segments ofpolymers such as mono-, di-, triblock, etc., arms of star polymersbefore coupling are conveniently measured by Gel PermeationChromatography (GPC), where the GPC system has been appropriatelycalibrated. For polymers of the type described herein, the appropriatestandard is a narrow molecular weight polystyrene standard. Foranionically polymerized linear polymers, the polymer is essentiallymonodisperse and it is both convenient and adequately descriptive toreport the "peak" molecular weight of the narrow molecular weightdistribution observed. The peak molecular weight is usually themolecular weight of the main species shown on the chromatograph. Formaterials to be used in the columns of the GPC, styrene-divinylbenzenegels or silica gels are commonly used and are excellent materials.Tetrahydrofuran is an excellent solvent for polymers of the typedescribed herein. Ultraviolet or refractive index detectors may be used.

Measurement of the true molecular weight of a coupled star polymer isnot as straightforward or as easy to make using GPC. This is because thestar shaped molecules do not separate and elute through the packed GPCcolumns in the same manner as do the linear polymers used for thecalibration. Hence, the time of arrival at an ultraviolet or refractiveindex detector is not a good indicator of the molecular weight. A goodmethod to use for a star polymer is to measure the weight averagemolecular weight by light scattering techniques. The sample is dissolvedin a suitable solvent at a concentration less than 1.0 gram of sampleper 100 milliliters of solvent and filtered using a syringe and porousmembrane filters of less than 0.5 microns pore size directly into thelight scattering cell. The light scattering measurements are performedas a function of scattering angle, polymer concentration and polymersize using standard procedures. The differential refractive index (DRI)of the sample is measured at the same wave length and in the samesolvent used for the light scattering. The following references areherein incorporated by reference:

1. Modern Size-Exclusion Liquid Chromatography, M. W. Yau, J. J.Kirkland, D. D. Bly, John Wiley and Sons, New York, N.Y., 1979.

2. Light Scattering From Polymer Solutions, M. B. Huglin, ed., AcademicPress, New York, N.Y., 1972.

3. W. K. Kai and A. J. Havlik, Applied Optics, 12, 541 (1973).

4. M. L. McConnell, American LabOratory, 63, May, 1978.

The composition of the present invention generally comprises 100 partsby weight of a bituminous component and from 8 to 15 parts by weight per100 parts of the composition of the radial block polymer describedabove. If less than 8 parts of the polymer of the invention is used,then the composition does not exhibit enhanced properties. If more than15 parts are used, the composition may be too high in viscositydepending upon the specific polymer structure and viscosity.

The compositions of the present invention may optionally include otheringredients like fillers such as ground tires or inorganic fillers liketalc, calcium carbonate and carbon black. The composition may alsoinclude resins and oils and other components such as stabilizers. It mayalso include other polymers, for example, other polymers of conjugateddiolefins.

Hot melt asphalt concrete compositions according to the presentinvention are especially advantageous. Hot melt asphalt concretecompositions according to the present invention will normally containfrom 80 parts to 99 parts by weight of aggregate and from 1 part to 20parts of a bituminous composition which is generally comprised of 90 to98 parts by weight per 100 parts of the bituminous composition of abituminous component and from 2 parts to 10 parts by weight per 100parts of the bituminous composition of one of the polymers discussedabove. If less than 2 parts of the polymer is used, there is little orno improvement in properties and if more than 10 parts of the polymer isused, then the composition is too costly and high in viscosity. Asphaltswith good flow resistance prior to polymer addition are preferred atvery low polymer concentrations because at very low polymerconcentrations the polymer does not contribute strongly to otherproperties such as rutting resistance. In other words, at low polymerconcentrations, asphalts with good rutting resistance on their own arepreferred.

Aggregate is basically rocks and sand. It is intended to be mixed withthe bituminous composition to form the hot mix asphalt concrete. Thebituminous composition is the binder which holds the aggregate together.

Roofing compositions according to the present invention are alsoespecially advantageous. In roofing compositions designed for rollroofing membranes a composition of 85 to 92 parts asphalt and 8 to 15parts polymer is preferred. As with HMAC compositions other additivessuch as inorganic fillers, resins, oils, and stabilizers may be added.

Similar compositions may be used for laminating adhesives and tabadhesives. For laminating or tab adhesives a composition of 90 to 96parts asphalt and 4 to 10 parts polymer is preferred.

EXAMPLES

Several blends of polymer and asphalt were utilized in the followingexperiments. In blends 1 through 4, the asphalt was a 100 pen flux andthe blends contained 20 percent talc filler. Blend 5 utilized a 200 penflux and 30 percent filler. All of the blends contained 12.5 percentweight polymer based on asphalt.

The polymers used are: Polymer A, a styrene-butadiene-styrene (SBS)linear block copolymer having a molecular weight of 110,000 and acoupling efficiency of 84 percent and a PSC (polystyrene content, %weight) of 30 percent and a styrene blockiness of 99%; Polymer B, a4-armed (SB) radial block copolymer with a molecular weight of 280,000and a coupling efficiency of 84 percent and a PSC of 30 percent and astyrene blockiness of 99%; Polymer C, a 4-armed (SB) radial blockcopolymer with a molecular weight of 220,000 and a coupling efficiencyof 95 percent and a PSC of 30 percent and a styrene blockiness of 99%;and Polymer D, a SB radial block copolymer with 4 arms, a molecularweight of 200,000, a coupling efficiency of 84 percent, a PSC of 23percent, and a styrene blockiness of 99%.

The blends were made by addition of polymer pellets to the asphalt at180° C. using a Silverson L4R high shear mixer to disperse the polymer.After 45 minutes, the polymer was fully digested. The filler was thenadded and stirred for 10 minutes. The blends were then tested forvarious properties. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        1                     3                                                       9.4% A       2        8.3% D   4      5                                       3.1% B       12.5% C  4.2% B   12.5% B                                                                              12.5% B                                 ______________________________________                                        Ring & Ball                                                                           119      119      113    --     125                                   softening                                                                     point (°C.)                                                            Pen (dmm)                                                                             39       38       32     --     41                                    Cold    -25      -25      -23    --     -25                                   bend (°C.)                                                             Vis @   3000     2600     3800   --     4700                                  190° C.                                                                (cps)                                                                         ______________________________________                                    

Desirable properties are a softening point of about 118° to 125° C., apen value of about 30 to 40 dmm, a cold bend temperature of less than-20° C., and a viscosity as low as possible.

Blend 1 exhibits typical good properties. Blend 1 is undesirable,however, because it requires a mixture of two polymers. This adds extrahandling and storage costs and increases the potential for error.Polymer A alone does not give a sufficiently high softening point.

Blend 2 is exemplary of the invention. All of the desired properties areachieved with a single polymer.

Blend 3 demonstrates another approach to reach the desired properties.Polymer D has high molecular weight, but lower than normal polystyrenecontent. The lower styrene content causes an unacceptable loss ofsoftening point while the viscosity is still high.

Polymer B did not form a stable blend in the 100 pen asphalt (Blend 4).This is symptomatic of high molecular weight polymers with high styrenecontent in hard asphalts. For illustrative purposes a blend of Polymer Bwas prepared in a softer asphalt. Even in a softer asphalt Blend 5 showsthe highest viscosity of any of the blends.

I claim:
 1. A bituminous composition comprising a compatible bituminouscomponent and a completely non-tapered radial block copolymer of aconjugated diolefin and a vinyl aromatic hydrocarbon wherein the blockcopolymer has from 3 to 6 arms, a molecular weight of from 150,000 to400,000, a coupling efficiency of at least 95 percent, and at least98.5% of the vinyl aromatic hydrocarbon is contained in the vinylaromatic hydrocarbon blocks.
 2. The composition of claim 1 wherein thepolymer comprises from 8 parts to 15 parts by weight of the bituminouscomposition.
 3. The composition of claim 1 wherein the polymer ishydrogenated.
 4. A hot melt asphalt concrete composition comprising:(a)from 80 parts to 99 parts by weight of aggregate, and (b) from 1 part to20 parts by weight of the bituminous composition of claim
 1. 5. The hotmelt asphalt concrete composition of claim 4 wherein the bituminouscomposition is comprised of:(a) from 90 parts to 98 parts by weight per100 parts of the bituminous composition of the bituminous component, and(b) from 2 parts to 10 parts by weight per 100 parts of the bituminouscomposition of the polymer.
 6. A roll roofing membrane comprising amembrane and the bituminous composition of claim
 1. 7. The roll roofingmembrane of claim 6 wherein the polymer comprises from 8 to 15 parts per100 parts by weight of the bituminous composition.